Foreign same-sex partners who wish to remain in the US are advised to submit proof of marriage to the State Department by December 31, 2018, or expect to leave the USA within 30 days of that deadline.

In a statement published on its website on October 1, the State Department has warned: "Effective immediately, USA embassies and consulates will adjudicate visa applications that are based on a same-sex marriage in the same way that we adjudicate applications for opposite gender spouses".

The justification for this move is that gay marriage is now legal in the US, so it's only fair that gay and straight couples play by the same rules.

In July, the US mission sent out diplomatic notes to the United Nations and representatives for foreign diplomatic missions explaining the new policy, which reversed a 2009 decision by then-Secretary of State Hillary Clinton to grant visas to domestic partners of USA and foreign diplomats.

"So it's especially difficult to understand why a country like United States would take a backwards step on this and make life even harder on same-sex couples for no apparent reason".

Since the 2015 Supreme Court decision legalising same-sex marriage, the United States policy has dictated that diplomatic visas are only extended to married spouses. Gay marriage is only legal in about 10 percent of the countries in the United Nations.

"Same-sex spouses of United States diplomats now enjoy the same rights and benefits as opposite-sex spouses", read the announcement obtained by Foreign Policy.

Ms Kumar said there are documented cases of death threats being sent to same-sex partners and their families who decide to marry overseas when the act is illegal in their home country.

Lawmakers and gay rights advocates are criticizing a new State Department policy that denies family visas to the same-sex domestic partners of diplomats posted in the United States and gives those already in the country three months to marry or lose their visas. But they could potentially be exposed to prosecution if they return to a country that criminalizes homosexuality or same-sex marriages.

But it also rolls back a practice championed by former Secretary of State Hillary Clinton to extend benefits to same-sex domestic partners of diplomats or worldwide staff posted in the USA, even if they were not legally married.

1, North Atlantic Treaty Organisation and G visas will only be given if the same-sex couple is legally married in their country of origin.

Straight couples have always needed to be married in order for the partner of a diplomats or United Nations official to receive a visa of their own.

A State Department spokesperson toldNBC News that the government's intention was "to help ensure and promote equal treatment" between straight and same-sex couples. He warned that some could be vulnerable to prosecution, and that it will create hurdles for couples considering a posting at United Nations headquarters in NY.

Former US Ambassador to the UN Samantha Power decried the policy, calling it "needlessly cruel and bigoted".